Gas lift is a commonly-used method for producing wells which are not self-flowing. Gas lift consists of initiating or stimulating well flow by injecting gas at some point below the fluid level in the well. In some gas lift operations, gas is conducted to the point of injection through an axillary string of tubing. When gas is injected into the formation fluid column, the weight of the column above the point of injection is reduced as a result of the space occupied by the relatively low-density gas. This lightening of the fluid column is sufficient in some wells to permit the formation pressure to initiate flow up the production tubing to the surface. Gas injection is also utilized to increase the flow from wells that will flow naturally but will not produce the desired amount by natural flow.
There are numerous gas lift arrangements, including various designs for flow valves which may be installed in the tubing string in open and inject gas in response to a predetermined pressure differential between the casing tubing annulus and the production tubing. When the valve opens, gas is injected into the tubing to initiate and maintain flow until the production tubing pressure drops to a predetermined value. The valve is set to close before the input gas/oil ratio becomes excessive. Other valve arrangements are designed to maintain continuous flow, proper pressure differential, and proper gas injection rate for efficient operation, and safety shut-down.